To be honest, the Han government was able to crush the power of local landholders once. But this statement can only apply in the early and mid times of the Western Han Dynasty. In the last decades of the Western Han, the government already lost the ability to fully control the local powers. From the Western Han Dynasty to the Jin Dynasty, there were 2 parallel trends. The power decline of the central government and the rise of landlords and finally led the Jin emperors became the weakest throughout Chinese history. Besides, the power base and nature of the Jin Dynasty was very different from the Han Dynasty. All these factors caused Jin's emperor could not handle the landholders just like Han's emperor did.

After the prolonged civil war, Liu Bang founded the Western Han dynasty. Because of the destruction and huge casualties, both the government and the people were weak. From Gaozu of Han to Wudi of Han, the Han government succeeded in reform and centralization. After the Rebellion of the Seven States, the central government began to rule directly into the east of Luoyang. And that's how the central government started to encounter the local landholders. Generally, the first 60 years of the Han dynasty were at peace. The adoption of private ownership of land and economic development inevitably gave birth to strong landlords. While the rich can provide well education to their offspring, many officials were landlords at the same time. During Wudi's era, which is the golden era of the Western Han Dynasty, the central government possessed enough power to crush and adjust this situation through the method of harsh treatment and forced migration. The successors of Wudi kept on using the aforementioned ways but they failed to stop the growth of local powers. The national strength of the Western Han Dynasty began to fall after it reached its peak in Wudi's era. During the reign of Emperor Yuan of Han and Emperor Cheng of Han, all forced migration plans were unsuccessful because the government was too weak. All they can do was compromised with reality.

In 9 A.D., Wang Mang ended the reign of the Western Han Dynasty and became the new ruler of China. His idealism was soon met with disaster. The empire was spiraled into chaos and discontent. The powerful landowners turned into warlords and built their own regime. The unifying war severely damaged the country. Liu Xiu, who was a noble and landlord, ended the war and rebuilt the Han Dynasty. Later he was called Guangwudi, the founder of the Eastern Han Dynasty. Although China was reunified, the new empire was brittle and powerless. The unifying war did not wipe out the power of landlords and they might become new threats of the Han government. To announce the power and prestige of the new ruler, Guangwudi decided to measure and collect data on population and farmland. His intension was clear, carefully identify the landlord's assets, and manpower. The policy then backfired, enormous revolts broke out in every corner of the empire. The newly-born empire lack of ability to suppress the armed forces. Without any alternative choice, Guangwudi reached terms with the landlords and recognized their rights. The empire gained peace again, but the relations between the central government and the landlords could never return to Wudi's days. History soon repeats itself. After a century, the Yellow Turban Rebellion crushed the rule of the Han government. The local officials caught the chance and became warlords during the wartime. Local landholders, who were scholars, literates, or intellectuals simultaneously, joined different camps and fight for the generals. The result of disputes was the usurpation of Cao Pi, who was the son of the famous Cao Cao. The Eastern Han Dynasty collapsed, at the same time, the Period of the Three Kingdoms begins. Landlords or you may say great families have always been a crucial political force in the kingdoms. The decline of the Three Kingdoms and the foundation of the Jin Dynasty were highly related to them. While the support of great families was the main source of legitimacy, the result of the civil war did not weaken but strengthen the power of landlords.

Since the Sima family was one of the most famous great families at that time, the Western Jin Dynasty still remain enough power to maintain its rule over the regime. However, after the death of Wudi of Jin, the founder of the Jin Dynasty, the empire went into the war of eight princes. The nomadic tribes seized the chance and invaded China. The Western Jin Dynasty fell after a short reign of 50 years.

During the event of Disaster of Yongjia, one of the noble members escaped to the South and rebuilt Jin Dynasty. By the support of Great Clans from North China and landlords of South China, Sima Rui, who later called Emperor Yuan of Jin, ascended the throne and became the founder of the Eastern Jin Dynasty. Since the Sima family did not have any power base in South China. The rule of Yuandi was reluctantly based on weak claim and legitimacy. Without recognition of the landlords, the emperor was impossible to continue his rule. This nature of the Eastern Jin Dynasty determined that the government could hardly defy the local landowners. This situation marked as the most specific feature of the Eastern Jin Dynasties and subsequent Southern Dynasties. Only after the rebellion of Hou-jing(548-552 A.D.), the relation between the emperor and local landholders reset to a stage that similar to the early days of the Western Han Dynasty. Since the revolts of Hou-jing led to the fall of great clans, the social structure of South China was completely deconstructed. The new ruler then obtained a greater ability to influence the local landholders.

Sources:

田餘慶(Tian Yuqing)：《秦漢魏晉史探微》(A study on the history of Qin, Han, Wei, Jin Dynasty)，中華書局，2011年6月

田餘慶(Tian Yuqing)：《東晉門閥政治》(Politics of Aristocrat Clans in Eastern Jin Dynasty)，北京大學出版社，2012年5月

陳寅恪(Chen Yinke)：《魏晉南北朝史演講錄》(Lectures on History of Wei, Jin, Southern and Northern dynasties)，貴州人民出版社，2012年1月

陳蘇鎮(Chen Suzhen)：《春秋與漢道-兩漢政治與政治文化研究》(Politics and Political Culture in Two Han Dynasties)，中華書局，2011年9月

To add the already excellent answer given, during the latter Han and certainly by it's end, the Han had problems with it's powerful families.

The latter Han empire had the misfortune of most rulers came to power as a child which meant a regency. If the Emperor survived to adulthood, the regent and/or the Dowager wasn't always willing to hand over power, this sometimes led to the Emperor gathering up what supporters he could and overthrowing the regent. The Emperor then would rule a short time, die without an heir (usually, at best a child heir) and so regency begins anew. Add dealing with various wars or issues of the day, Emperor's didn't have the time or the personal authority to rebuild the tax system (that was no longer providing enough money by the 140's) while they struggled to deal with the increasing violence from powerful families with their retainers engaged in vendetta's or a recruitment system that was in the hands of the powerful. Measures taken to deal with such matters would arouse protest and Emperor's would try to win support or at least maintain a balance with the powerful families.

By the end, Emperor Huan and Emperor Ling both used the eunuchs (who had repeatedly come to Emperor's aids against the regents whereas gentry had been implicated in the regicidal regime of Liang Ji) to act as a counter-balance at the capital and in the provinces via their own retainers and families. This went down badly with the gentry who saw them as unnatural beings who should never be given power and disliked the challenges to their powerbases. This worsened tensions with some bloody reprisals from both sides while the ill-suited Emperor Ling drove the long declining Han into the ground.

A few months after Emperor Ling's death in 189, the land spiraled into civil war as tensions in the capital exploded, the eunuchs (and many many others) were slaughtered and frontier general Dong Zhuo took advantage of power vacuum at the capital. Alarmed by Dong Zhuo several gentry leaders fled the capital and raised armies, starting a long and brutal civil war. These warlords did have to keep an eye on the gentry in all sorts of ways, Andrew Chittick Life and Legacy of Liu Biao for example talks of how the northern and the southern interests of the Jing gentry shaped his rule. However I will focus on Wei and Wu whose gentry struggles mattered for Jin.

Jin united the land eventually but the Sima family were not one of the starting warlords: they came into ruling power via the 249 coup against fellow Wei regent Cao Shuang by Sima Yi and then the Sima's didn't let go until the last Wei Emperor Cao Huan abdicated to Sima Yan to 266.

Wei under the Cao family had sought to have some distance from the gentry with things like marrying outside those circles but without distancing themselves too far. However the gentry had become uneasy at Emperor Ming/Cao Rui's (reigned 227-239) big spending and eccentricities (clothing, giving jobs to females) while they had long objections to Cao's centralizing power. Cao Rui died young leaving an child (Cao Fang) as an heir and botched succession plan with the wily Dowager Guo, the diligent Cao Shaung and the senior offical Sima Yi.

The two regents eventually fell out and Cao Shuang outmaneuvered Sima Yi. His regime became associated with the neo-Doaist libertine He Yan, part of a new wave of scholars who were rebelling against the conventions and usual proprieties, confirming the "moral decline" of the Cao family. The old guard were not pleased by this or that He Yan and co attempted to reform the recruitment system away from the hands of the gentry who had taken control of the process. Sima Yi on the other hand was the descendant of a King so of very old family, Confucian, one of the old guard, a successful general and when Cao Shuang was out of the capital, he rose from his faked sickbed and seized control with the help of the old guard.

The Sima's would face rebellions from the generals (the coup saw the internal situation become unstable), the wiles of Dowager Guo, Wei loyalist ploys and an Emperor marching against them over the next 15 years. Sima Yi had taken power with the vital support of the gentry and his sons Shi+Zhao continued to need their support. They didn't fix the recruitment system, they put agricultural garrisons in the hands of the gentry and a less centralized state which pleased their supporters but meant power seeped from throne to the powerful families.

When the Sima's fled south, the southern landowners they were now with had had become very powerful under the Sun clan of Wu during the three kingdoms. The south had been built up by likes of Sun Quan and his ministers but central control had become increasingly weak as he grew old then when the Sun clan had a series of internal palace coups and counter-coups. The southern magnates killed the northern families after the fall of regent Zhuge Ke, a system that meant key families inherited rank, key positions (like Bu family had Xiliang), resources and soldiers.

So instead of the court controlling the allocation of resources, soldiers, sending new figures to take control of key points when need to be, the Sun rulers (or the regents) increasingly had to try to coax the magnates to help them which they were not always inclined to do. When the last ruler Sun Hao, given the throne as an emergency measure, tried to reassert some control, relations became very toxic with the powerful figures and he had limited success before his surrender. After Wu fell, Jin's lack of central control and pro-gentry policies would have also suited them and the likes of the Lu clan served the Sima's as they had the Sun's.

So they were unlikely to have been receptive decades later to the fleeing Sima's trying to assert control.

Sources: Rafe De Crespigny's 2003 The Three Kingdoms and Western Jin A History of China in the Third Century A.D,

Generals of the South (1990)

Fire Over Luoyang (2016)